1. Field of the Invention
The present invention relates to an ink jet recording apparatus and an ink jet recording method with an improved ink jetting property.
2. Description of the Related Art
As digital cameras and computers are more widely disseminated in recent years, a rapid progress has been made in hard-copy-image recording method for recording images obtained by these instruments onto paper or the like. An ultimate object of the hard copy resides in how to make an image quality be close to that of silver-salt photograph, particularly in gamut of color reproduction, color density, texture, resolution, glossiness, light resistance or the like.
The hard-copy recording system includes not only those directly taking a photograph of an image appeared on a display by silver-salt photographing, but also a vast variety of recording systems such as sublimation heat-sensitive transfer system, ink jet system and electrostatic recording system.
Of the above-mentioned recording systems, the ink jet recording system has been making a rapid progress in various fields because it can record high-definition images using a relatively simple apparatus. Printers that employ the ink jet recording system are manufactured in a wide variety of fields, and there are also a wide variety of inks corresponding to the purpose of use.
The ink jet recording apparatus used in the ink jet recording system is configured so as to allow ink droplets to fly (be jetted) while laterally reciprocating a recording head having a plurality of nozzles mounted thereon, to thereby form an image (pattern) according to image data on a recording medium which is typically a plain paper, special coated paper or the like in synchronization with movement of the recording medium.
The ink jet recording method is however disadvantageous in that it is slower in the recording speed than the electrophotographic system or fusion thermal transferring system. Efforts for solving the problem have therefore been made through increase in the driving frequency per one nozzle, or through increase in the number of nozzles per one color, and these efforts have been rapidly improving the recording speed. The increase in the number of nozzles per one color, however, raises the load in terms of cost, and the increase in the driving frequency degrades ink jetting property to cause a problem such as causing a bend of the flight direction of the droplets easily, where the bend becomes more remarkable when the driving frequency exceeds 15 kHz, and this is causative of streak-like unevenness when printing a uniform image.
On the other hand, there are various inks used for the ink jet printing system, which are classified depending on solvents or coloring materials used therefor into water-soluble dye ink, oil-soluble dye ink, water-base dispersion pigment ink, oil-base dispersion pigment ink or the like, and are selectable depending of applications. In particular, the water-base dispersion pigment ink is featured by its low impact on the environment through the use of water or water-soluble solvent as the main solvent and by its relatively large light resistance through the use of pigment as the coloring material. Thus, the water-base dispersion pigment ink became more widely used ranging from a system for producing posters or electric decoration to a printer for office use. However, the pigment inks has a drawback that they are more likely to cause clogging in the nozzle as compared with the dye inks.
Inventors of the present invention analyzed the above-described problems, and found out that the degradation of the ink jetting property was largely affected by characteristics of an ink supply tube disposed between an ink cartridge and an ink jet recording head. More specifically, it be came clear that air bubble which attaches on the inner surface of the ink supplying tube, or a component of the ink which runs through the ink supplying tube deposits and attaches on the inner surface of the ink supplying tube as foreign matter. Therefore, the ink jetting stability is affected.
Various methods have been proposed in order to solve the problems on the ink jetting property. For example, Japanese Laid-Open Patent Publication No. 7-223322 discloses an approach of subjecting the ink supply tube to ozone treatment to thereby improve the ink wetting property thereof and make it possible to expel the air bubbles. Japanese Laid-Open Patent Publication No. 7-266572 proposes a method of selecting a material in which an adhesion work expressed by surface tension of the ink and a contact angle between the material for composing ink supply system and the ink is lower than or equal to a specified value in order to prevent the ink adhesion at the ink contact portion in the ink supply system. Japanese Laid-Open Patent Publication No. 8-156276 discloses a method of reducing adhesiveness of air bubbles by controlling the contact angle of the ink to the ink supply tube to as small as 10° or less. Japanese Laid-Open Patent Publication Nos. 2000-211149 and 2001-162817 further propose that the ink wetting property is improved by subjecting components of the ink supply system to ozone treatment or hydrophilization using polymers.
On the other hand, there are proposed methods of limiting the contact angle of the ink to plastic components of the ink supply system within a specific range (Japanese Laid-Open Patent Publication No. 2000-141692 (p. 1) and Japanese Patent Publication No. 3033190 (p. 2)). It is, however, difficult to obtain a stable ink jetting property only by controlling the contact angle of the ink to the components of the ink supply system, particularly in a high-speed ink jet recording system such as having a driving frequency of the recording head of as high as 15 kHz or above as described above, so that there are demands for further improvement.